<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .container {
      position: relative;
      width: 400px;
      height: 400px;
      background: #fff;
    }
    .container .bg {
      position: absolute;
      top: 50%;
      left: 50%;
      transform: translate(-50%, -50%);
      width: 100px;
      height: 100px;
      border-radius: 50%;
      background: red;
    }
    .container .round1 {
      position: absolute;
      top: 50%;
      left: 50%;
      transform: translate(-50%, -50%);
      width: 100px;
      height: 100px;
      border-radius: 50%;
      box-shadow: 0 0 20px 0 #ddd;
    }
    .container button {
      margin: 50px 30px 100px;
    }
    .water {
      animation: amWater 3s ease infinite;
    }
    @keyframes amWater {
      0% {
        transform: translate(-50%, -50%) scale(.5);
        opacity: 1;
      }
      33% {
        transform: translate(-50%, -50%) scale(1);
        opacity: .7;
      }
      66% {
        transform: translate(-50%, -50%) scale(1.5);
        opacity: .3;
      }
    }
  </style>
</head>
<body>
  <div class="container">
    <div class="round1"></div>
    <div class="bg"></div>
  </div>
  <div class="container">
    <button class="animation-start">开始</button>
  </div>
</body>
<script>
  const elmStart = document.querySelector('.animation-start');
  const elmRound = document.querySelector('.round1');
  elmStart.addEventListener('click', function() {
    elmRound.classList.add('water');
  })
</script>
</html>